1. Field of Disclosure
The disclosure relates to high power fiber laser systems. In particular, the disclosure relates to a clad mode stripper (“CMS”) operative to remove undesirable high power cladding-guided light during a switch-on phase of system operation.
2. Prior Art
At high optical power levels of single mode fiber laser systems, based on a double clad fiber, which includes a core, inner cladding and outer protective polymer and is operative to emit output beam of the order of tens of kilowatts in substantially a single mode operation, the task of managing stray light propagating along the inner cladding becomes crucial. Even a small fraction of stray light in the cladding can heat a protective polymer to damaging temperatures and cause a catastrophic failure of the fiber.
High thermal stresses generated by a rapid temperature rise during the initial, switch-on operational phase of a high power fiber laser system, when the system's output increases from 0 watt to the desired high power, are particularly damaging to double-clad fibers which are used in kW-level fiber laser systems. Typically, a time period associated with the switch-on phase does not exceed about 100 milliseconds and characterized by a localized decoupling of clad modes at the upstream end of the fiber. Accordingly, the cladding modes need to be safely removed which is typically realized by a clad mode stripper (“CMS”) the known configurations of which are briefly discussed hereinbelow.
One of numerous CMS configurations includes a small strip of high index silicone placed over the inner low index cladding along upstream end of a fiber which is stripped from the protective polymer. However, because the coupling is localized and the length of the coated high index silicone is short, the latter is often overheated and decomposed.
A need therefore exists for a device minimizing thermal stress during the switch on phase of a high power fiber laser system.